Metal’s metamorphosis

By Gretchen Salois

Researchers continue to uncover metal properties and capabilities

February 2013 - Metallurgists have been trying to make the grains of metals smaller, which will make them stronger without affecting other properties or making them difficult to machine. Christopher Schuh Ph.D, Head of the Massachusetts Institute of Technology’s Department of Materials Science and Engineering, says researchers are uncovering how to increase metal strength without compromising other factors.

“If you get the grains small, you get high strength, but if the grains get nanoscale enough, you get new types of physics, comprising not only the properties of the metal grains but the interfaces between them, resulting in new nanophysics,” Schuh says. “Recent research offers new opportunities to deliver new combinations of properties.”

The interest in this field is long-standing. “Ten years ago, there were a lot of people doing what I call proof of concept work, working with metals with really fine nanoscale grains in them,” he explains. “Very little of what was produced was stable. People could make a nanocrystalline metal, but the grain structure would grow and it was no longer nano anymore.”

Schuh’s team developed new alloying science, making grain structure not transient or fleeting but stable and permanent. By combining tungsten and titanium. “We were looking for a nanocrystalline tungsten that would be stable at high temperatures, heating it to 1,100 degrees Celsius,” Schuh explains. “We want to retain the nanoscale structure at these very high temperatures. We found that what we could add to tungsten should bring the desired result. Knowing how long trial-and-error would take, we used theory to identify a combination that we felt might work.”

From research to reality

The implications for the metals industry are great. Schuh’s team tried to develop a tungsten-based alloy that is heavy and strong. “You can apply this concept to many different metals; we’re systematically using our thermodynamic approach to find other interesting options,” he says.

According to an article by Julia R. Weertman, a professor at Northwestern University, “Retaining the Nano in Nanocrystalline Alloys,” available at www.sciencemag.org, further research needs to be done to produce a nanocrystalline alloy that is “thermodynamically stable, not just metastable, and considerable effort has gone into achieving this goal.”

This latest research is one segment in a long line of information, much of which already is used in today’s metals industry. “Some of the things we’ve done at MIT are already in use in billions of components like coatings—the metals industry has already incorporated some of these things and those products are already out there in the market,” Schuh says.

During a time when companies are working toward lightweighting everything from cars and trucks to airplanes, Schuh says his team has made developments in lightweighting aluminum alloys, currently being explored by companies but not necessarily made available yet to the public. “Developments have extended beyond the MIT research and development umbrella to corporations elsewhere,” Schuh says.

There are thousands of metallurgists researching the many facets of different metals bringing, “not only new alloys but a new way of thinking about these alloys,” Schuh says. “It’s a new way of thinking about how to design an alloy so the next generation products can cash in on some new physics we maybe weren’t thinking of before.”

There currently are many different projects “all on parallel trajectories,” says Schuh. “We’re developing entire new families of new materials, and we have more work coming out in tungsten.

“To be honest, we’re at the beginning of exploring this concept and there are hundreds more design projects to be had in the space,” he continues. “This is a long-range project where we’re trying to rethink metals design. We want to improve the performance of the metals and allow those in the metals industry to rethink the properties of their own particular metal—research continues and new combinations are in the works.” MM

Sources

Schuh Research Group at MITCambridge, Mass.phone: 617/253-1000www.mit.edu